If that's the only entry in your SPN table, then you will need to look at your NPA table.
1. Turn on capture to a file your TTY emulation program
2. >ld 90
REQ prt
CUST 0
FEAT net
TRAN ac1
TYPE npa
Capture your entire NPA table to a file.
3. Edit the file and search for NPA entries containing 800, 888, 877, 866 entries; these may be 1888, 1877, etc.
4. Create a new NPA entry for 855 prefixes.